Various technologies for monitoring robots have been developed. For example, each of PTLs 1 and 2 discloses a technology in which: a force sensor is provided at a tip end of an arm of a robot; and an abnormality of the robot is monitored based on information detected by the force sensor. Further, each of PTLs 3 and 4 discloses a technology in which: a predetermined area is set in an operating range of a robot; an abnormality of an operating speed of the robot in the predetermined area is monitored.
From the viewpoint of productivity improvement, proposed in recent years is that a robot and an operator work cooperatively in the same work space. Therefore, from the viewpoint of safety, for example, PTL 5 discloses a technology in which: a predetermined area is set in an operating range of a robot; and when it is detected that a person has entered into the predetermined area, the robot is operated at low speed.